1. Field of the Invention
Aspects of the present invention generally relate to a stereoscopic image capturing system and a lens device.
2. Description of the Related Art
Conventionally, in the film production industry, more realistic images have been demanded. Especially, in recent years, demands for stereoscopic images capable of expressing an image having a sense of depth have been greatly increasing. In the stereoscopic image capturing operation, in addition to the control of angles of view and in-focus positions which can be controlled in conventional image capturing, the control of a sense of depth of images is required.
The methods of controlling the sense of depth include a method of controlling the base-line length (the distance between the optical axes of two image capturing apparatuses) and the convergence angle (the angle between the optical axes of the two image capturing apparatuses) of the two image capturing apparatuses. More natural stereoscopic images can be captured by operating the apparatuses similarly to the movements of human eyes. Consequently, in general, the base-line length of the two image capturing apparatuses is fixed, and the convergence angle is controlled.
To control the convergence angle, a method of rotating the entire of the image capturing apparatus around an axis in the direction perpendicular to the optical axis, and a method of shifting an optical element such as a mirror and a prism to bend the light beam are proposed. Unfortunately, the above-described methods cause increase in the sizes of the structures of the image capturing apparatuses. In addition, the imaging capturing apparatuses are exclusively used for stereoscopic image capturing, and lack general versatility and usability.
To solve the problems, for example, Japanese Patent Application Laid-Open No. 2008-028900 discusses a method of controlling a convergence angle using an optical element (hereinafter, also referred to as “shift lens”) provided for image blurring correction, the optical element moves within a plane perpendicular to the optical axis.
Japanese Patent Application Laid-Open No. 2010-103895 discusses a method of correcting image blurring while adjusting a convergence angle by driving shift lenses based on a value acquired by adding an amount of movement of the shift lens for adjusting the convergence angle and an amount of movement of the shift lens for correcting image blurring.
Although the shift lens is used for the convergence angle control (control in the optical axis direction), it is useful to use the shift lens for image blurring correction that is an original function of the shift lens.
However, in the known image capturing apparatuses discussed in Japanese Patent Application Laid-Open No. 2008-028900 and Japanese Patent Application Laid-Open No. 2010-103895, the driving units for correcting image blurring are also used as the driving units for controlling the convergence angles. Consequently, the mechanism is not expected for the use of adding an amount of drive for the convergence angle control to an amount of drive for the image blurring correction. As a result, when the amount of drive for the convergence angle control is added to the amount of drive for the image blurring correction, at the side the amount of drive for the convergence angle correction is added, a movable area wide enough to drive the optical element (shift lens) is not secured.
In such a state, if the value acquired by adding the amount of drive for the convergence angle control to the amount of drive for the image blurring correction is directly used to drive the optical element, due to mechanistic limitations in the movable region, only at the side the amount of drive for the convergence angle control, the optical element may not be fully driven. As a result, images that are not completely stabilized only in a particular direction and giving very uncomfortable feeling are acquired.
To solve the problem, even if the movable region of the optical element is simply widened to enable the driving unit to be driven without limiting the amounts of drive for the image blurring correction and the convergence angle control, the problem is not solved. This is because as the optical element shifts more, the decentration aberration increases further, and as a result, it is difficult to maintain the optical performance.